The present invention concerns a new agent for sizing in the paper industry, more particularly for paper and cartons, consisting of a cationic polyurethane dispersed in water in the form of a latex and its method of manufacture.
Cationic polyurethanes already are the subject of patents. It is, for instance, known to prepare a quaternary ammonium compound from a prepolymer with NCO terminal groups, obtained by the addition of a polyisocyanate to a dihydroxylated aliphatic monomer compound, elongated by an aliphatic diol containing a salifiable and/or quaternizable tertiary nitrogen atom. That is the case, for instance of French Pat. No. 2,256,937.
Cationic polyurethanes are described in French Pat. No. 2,322,236 which are reaction products of polyisocyanates of the diphenylmethane series and N-alkyldialkanolamines of the C.sub.5 -C.sub.12 series whose alkyl chain contains C.sub.1 -C.sub.6 and possibly reactive groups serving as chain terminators, polyurethanes carrying protonized and/or quaternized ammonium groups, in solution in water and utilized for the sizing of paper. These products, of low molecular weight and although hydrophilic, are recognized by their inventors as efficient, as compared to the cationic products for paper sizing known previously.